The important thing to know is that you have to generate your classes with one schema each time. If you put webapp schemas 2.2 and 2.3 in the same time,
you will obtain errors. Be sure to include all the files related to your webapp schema to generate your java classes.

Example : webapp 2.4 need
web-app_2_4.xsd
j2ee_1_4.xsd
jsp_2_0.xsd

You can even do some customization with a config file named : domain.jaxb (/src/main/resources).